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Polarized Neutrons in ANSTO – From LONGPOL to Pelican, Taipan, Sika, Platypus and Quake

Polarized Neutrons in ANSTO – From LONGPOL to Pelican, Taipan, Sika, Platypus and Quake. Dehong Yu and Shane Kennedy Bragg Institute, ANSTO, Australia. Polarizer. Spin flipper. LONGPOL – (1973-2005). Flipper drive pulse sequence. Intensity variation for non-spin-flip scattering.

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Polarized Neutrons in ANSTO – From LONGPOL to Pelican, Taipan, Sika, Platypus and Quake

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  1. Polarized Neutrons in ANSTO – From LONGPOL to Pelican, Taipan, Sika, Platypus and Quake Dehong Yu and Shane Kennedy Bragg Institute, ANSTO, Australia

  2. Polarizer Spin flipper LONGPOL – (1973-2005)

  3. Flipper drive pulse sequence Intensity variation for non-spin-flip scattering Intensity variation for spin-flip scattering Cross-correlation of intensity with drive sequence LONGPOL – Energy Analysis Modulation of neutron polarization using pseudo-random pulse train to drive spin flipper, Cross-correlation of intensity with the drive sequence • Direct separation of spin-flip and non-spin flip scattering. • TOF – energy analysis

  4. Lessons from LONGPOL • Fix Geometry means non-flexibility • Compact design means • Difficulty to access • Limitation to different sample environment • Low flux, long data acquisition time • Statistic chopper • Relative high background • Only works well for strong signals

  5. Taipan (TAS) Echidna (HRPD) Wombat (HIPD) Koala (QLD) Sika (CTAS) Platypus (Ref) Kowari (RS) Quokka (SANS) New Instruments in OPAL Pelican (TOFPAS)

  6. Pelican - TOFPAS

  7. TOF-PAS Preliminary Specifications • Design goals: • Inelastic & quasi-elastic neutron spectroscopy • – time focusing TOF spectrometer (Comparable w/- IN6 @ ILL) + • Polarization analysis capability (Comparable w/- D7 @ ILL) • Preliminary Specs. – to reach the design goals • Neutron Wavelength: 2.4 Å – 6.3 Å, (14.2 meV – 2.1 meV) with HOPG • Energy resolution: 50 µeV to 350 µeV (~2.5%) • Q range: 0.05 Å-1- 5 Å-1 • Solid angle: ¾ Steradians (non-pol), ¼ Steradians (pol) • Neutron flux at sample: ~ 8 x106 n/cm2/s at 3.7 Å, (full beam)

  8. Current Status - Stage 1 5.4 metre • Dance floor installed • Monochromator shield installed • Monochromator stage ordered, Beam Monitor ordered

  9. Stage 2 • Phase 1 - Conceptual Design • General considerations • Multiple HOPG monochromator (vertical or double focusing), mosaic about 0.5o • Wavelength filter: Cold Beryllium filter for λ above 4.1 Å and a HOPG diffraction filter for λ < 4.1 Å. • Beam Chopper: Double Stage Fermi Chopper • Sample stage: standard A-Z system • Collimation system (before and after sample) • Detector: 250 PSD 3He tube (Φ = 12.5 mm and length = 1m), cover about ¾ Steradian (3.125 m2) • Spectrometer Tank: Vacuum or Ar gas filled • Energy resolution: DE/Ei = 2.5% (50µeV to 300 µeV)

  10. Polarization Analysis • Polarizer: Supermirror bender • Spin Flipper: Mezei flipper; • Analyzer: Supermirror bender, and 3He polarizing filter is also considered if it becomes available in ANSTO. • Guide field: Two big magnetic coils cover the whole experimental area Polarizing bender Analyzing bender: (8 elements)

  11. Polarization Analysis

  12. Budget Estimation – Stage 2

  13. Project Schedule • Stage 1: Front End • Monochromator shield, stage and dance floor • Stage 2: Whole Instrument • Schedule: • Standard components • (stage 1) • Conceptual design • Engineering design • Manufacture & procure • Assemble & install • Commissioning

  14. -TAS Incident E: 5 meV – 120 meV Energy Transfer: up to 80 meV Scattering angle 2Өm: 15o – 85o Analyzer scattering angle 2ӨA: -110o – 110o Double focusing Mono. and Analyzer.

  15. TOF-Neutron Reflectometer Horizontal sample Solid –solid Liquid – solid Polarization option

  16. Dl= 3 to ~17 Å RF spin flippers before & after sample (Non-magnetic) m=3 supermirrors iron yoke Elevation looking along the beam 50 mm Permanent magnets adsorbing borated glass Transmission Polarizer – Ref. and SANS 1200 mm (m=3) FeSi polarizing supermirror on both sides of thin Si wafers Elevation perpendicular to the beam

  17. 5 Tesla cryo-free cryo-magnet (N.Z. design for Reflectometry/SANS) Under design Cryo-free cryo-furnace 4 K  800 K Arrived One system is commissioned Liq. He cryostat 1.4 K  300 K Arrived 7.4 Tesla cryo-free cryo-magnet Commissioned in ANSTO HMI’s 15 Tesla cryomagnet. Proposed Sample environments • 3He cryostat insert ~300 mK • Dilution refrigeration ~30 mK

  18. TOF-PAS Taipan Sika TOFPAS - (Q,ω) Molecular & lattice vibrations Spin waves Heavy fermions Molecular rotations Critical scattering

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